Joseph buys some heating oil. He puts it in his oil tank.
The scales show the numbers of litres of oil in the tank immediately before and immediately after Joseph puts the oil in the tank.
The oil Joseph buys costs 0.40 euros per litre.
Work out the total cost of the oil that Joseph buys.

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?